Preparation And Application Of Compound Nucleating Agent Graphene/Calcium Pimelate For Polypropylene

In recent years,with the increasing of market demand of high-performance nucleating agent for polypropylene(PP),and the development of highly efficient nucleating agent is more and more difficult,the speed of research and development for new products is slower.Therefore,a new type of complex nucleating agent which is more efficient than single nucleating agent has become hot spots of research and development.In this paper,a novel compound nucleating agent was prepared by combining calcium pimelate with graphene(named as Gra/CaHA)through the chemical bond to improve the dispersibility of graphene in PP.This compound nucleating agent can induce considerable content of β phase of PP so that the impact toughness of PP was increased significantly and the presence of graphene increased the rigidity of polypropylene at the same time.Three kinds of calcium pimelate were prepared by meta-decomposition reaction,neutralization reaction and mixing pimelic acid with calcium stearate(nalmed as D-CaHA,N-CaHA and S-CaHA,respectively).Fourier transform infrared spectroscopy(FT-IR)and differential scanning calorimetry(DSC)were used to study the structure and melting characteristics of prepared calcium pimelate,and the crystallization and melting behavior of polypropylene nucleated with those calcium pimelate was also researched by DSC.The results showed there is no free carboxyl group in the all of calcium pimelate prepared by the three methods.Calcium pimelate is not a pure substance but a coordination system consisting of pimelic acid and calcium ion and the system does not have a fixed melting point.D-CaHA,N-CaHA and S-CaHA increased the crystallization temperature of polypropylene by 4.9 ℃,4.9 ℃ and 6.5 ℃,respectively.It was also found that S-CaHA inducted more P crystal polypropylene than D-CaHA and N-CaHA.The compound nucleating agent Gra/CaHA was connected together by chemical bond rather than mechanical mixing.Gra/CaHA improved the crystallization temperature of PP significantly.Under the same addition amount,the crystallization temperature of PP nucleated with Gra/CaHA is higher than that of PP nucleated by mechanically mixed graphene and calcium pimelate(named as Me-Gra-CaHA).Gra/CaHA increased the crystallization temperature of polypropylene by 8℃ while Me-Gra-CaHA increased by only 5.9℃.The relative content of β-modification of polypropylene can be obtained from the data of the WAXD curves and DSC curves.It could be seen that the β crystal content was different between those two research methods(57.0%by DSC method and 86.8%by WAXD method)because of the β-α transition in the DSC.